Transfusion therapy in the past was largely dependent on the use of whole blood. While whole blood may still be used in certain limited circumstances, modern transfusion therapy depends largely on the use of clinically needed blood component. Whole blood consists of many components, primarily, red blood cells, white blood cells, platelets, and plasma. Therefore, a whole blood unit that is collected from a normal donor can be processed to separate it into its components. Each component can then be transfused to a needy individual.
Centrifugation is a known technique for separating blood into its individual components. This is possible because each blood component has its own density. Therefore when whole blood is subjected to high centrifugal force, the components of different densities are separated. When a whole blood container is placed in a rotating centrifuge, red blood cells (RBC) of the highest density are concentrated in a section of the container that is the most distant from the axis of rotation of the container. White blood cells (WBC) having the second highest density are concentrated in a layer supported by the RBC layer and are positioned closer to the axis of rotation. Platelets with a density slightly less than that of the WBC are clustered in a layer adjoining the WBC layer closer to the axis of rotation. Plasma with the least density is packed in a layer the closest to the axis of rotation.
At high centrifugation speed (hard spin), the blood is separated into three layers, an RBC layer, a mixture of WBC and platelets called “Buffy Coat” layer, and a plasma layer. At low centrifugation speed (soft spin), blood is separated into two layers, RBC and platelets rich plasma (PRP). A sharp and distinct edge is formed at the boundary of the separated RBC layer and PRP layer. These sharp edges are maintained by constant rotation of the centrifuge, and rapidly disintegrate when the centrifuge stops rotating.
Current blood separation techniques that are widely used in blood banks start by spinning a whole blood containing bag at a low speed in a large centrifuge. Distinctive RBC and PRP layers are formed in the blood (primary) bag. The centrifuge is then stopped and the primary bag is carefully removed from the centrifuge and placed in an extractor. The difficulty in this step is not to disturb the separation edge between the two layers. The PRP is manually squeezed out of the bag into an empty satellite bag connected to the primary bag. The RBC remaining in the primary bag is mixed with additive solution to preserve the RBC for storage. In most applications the RBC and additive solution mixture is directed through a leukocyte reduction filter to remove the white blood cells (WBC) from the RBC concentrate.
The satellite or auxiliary bag containing the PRP is then placed in the centrifuge and spun at a higher speed until the platelets are sedimented and a concentrated platelet layer and platelets poor plasma (PPP) layer are formed. The bag is carefully removed from the centrifuge without disturbing the separation edge and placed in a manual extractor. The PPP is expressed into a second satellite or auxiliary bag connected to the first satellite bag, leaving a platelet concentrate in the first satellite bag.
This current technique is labor intensive where human factor has imperative effect on product quality and purity. Contamination (unwanted RBC or WBC mixed with plasma or platelets) is a known threat to product quality. Among the reasons that cause platelets rich plasma contamination are the tendency of the top portion of the blood bag to fold during centrifugation and entrapping RBC. Following centrifugation, the entrapped blood cells can be released into the previously separated platelet-rich plasma. Another source of contamination of the PRP is the tendency of the bags contents to swirl during rotor deceleration in an effort to preserve its angular momentum causing RBC and WBC to be mixed with plasma.
Furthermore the handling of the blood bag after centrifugation and the way it is placed it in the extractor may cause contamination of the plasma by RBC or WBC.
More recently, automated extractors have been introduced in order to facilitate the manipulation of whole blood units. Nevertheless, the whole process remains laborious and requires the transfer of separated components from the primary bag to a satellite bag, to be completed quickly with manual intervention before disintegration of the separation edge in order to maintain product purity.
Moreover, the overall blood separation process has to be completed and the separated components have to be used or stored under appropriate conditions within a certain period of time after the blood collection to guarantee the quality and the medical integrity of the blood components. This time limit requires all blood processing procedures to be conducted efficiently and effectively in an environment heavily dependent on human factor and manual operations.
There have been many attempts to automate blood processing and transferring separated components from one bag to another while the centrifuge is rotating.
U.S. Pat. No. 4,447,220 discloses one method of placing a blood bag in a centrifuge rotor to separate RBC or plasma, and then displace RBC or plasma to a connected satellite bag by squeezing blood bag using a pressure pad, or by centrifugal force while the centrifuge is spinning.
U.S. Pat. No. 6,261,217 discloses a method of separating whole blood into RBC, plasma, and buffy coat by spinning a flexible disk.
U.S. Pat. No. 5,770,069 discloses a method and apparatus for separating blood components and washing or glycerolizing RBC by spinning multiple bags
U.S. Pat. No. 3,211,368 discloses a method and apparatus for blood separation and treatment of separated components including RBC washing and Glycerolization.
U.S. Pat. No. 6,605,223 discloses a method and apparatus for separating several units of blood into components by spinning cassettes containing multiple bags.